Stabilization of water soluble surface active agents



United States Patent 3,369,304 STABILIZATIUN OF WATER SOLUBLE SURFACE ACTIVE AGENTS Sidney G. Clark and Harold E. Feierstein, St. I. .ouis, M0., assignors to Monsanto Company, St. Louis, Mo., a corporation of Delaware No Drawing. Filed June 1, 1966, Ser. No. 554,329 Claims. (Cl. 34-9) This invention relates to the stabilization of water soluble alkyl polyoxyalkylene ethers. More particularly, it relates to the stabilization of water soluble alkyl polyoxyalkylene ethers by the incorporation of minor amounts of certain classes of compounds to be hereinafter described.

The alkyl aryl polyoxyalkylene ethers, generally produced by the condensation of an alkylene oxide such as ethylene oxide with certain branched chain alkyl phenols such as dodecyl phenol, have been widely used as nonionic surface active agents. The alkyl aryl polyoxyethylene ethers, however, are not as readily biodegradable as may be desired in some instances. The alkyl polyoxyalkylene ether surfactants are readily biodegradable and exhibit excellent detergent activity and are replacing the alkyl aryl polyoxyalkylene ethers. However, these compounds tend to degrade when dried with air under high temperature conditions, that is, at temperatures above about 100 C. and thus pose a problem in most heat drying operations. The problem is particularly acute when the alkyl polyoxyalkylene ethers are exposed to heat and air for prolonged periods of time such as when the material cakes inside a spray tower.

In accordance with this invention, it has been discovered that the alkyl polyoxyalkylene ethers can be stabilized by incorporating at least about 500 ppm. by weight based upon the weight of the alkyl polyoxyalkylene ethers of certain classes of compounds to be hereinafter described.

The alkyl polyoxyalkylene ether surfactants can generally be represented by the formula wherein R is an alkyl radical containing from about 6 to about 24 carbon atoms, Z is selected from the group consisting of H, S0 and P0 n is an integer from 2 to 4, x is an integer from 1 to 2, m is an integer from 1 to 29 when x is 1, and m is an integer from 1 to 14 when x is 2. Although this invention is independent of the method of manufacturing the alkyl polyoxyalkylene ethers, it has generally been preferred to produce these surface active agents by the condensation of an alcohol with alkylene oxide. The R group in Formula A, therefore, is derived from the alcohol when such a process is used. The alkyl polyoxyalkylene ethers which have been found to give suitable surface active properties generally contain an R group which has from 6 to about 24 carbon atoms. It has been found that when R contains from about 9 to 18 carbon atoms these compounds have preferred properties. It is to be noted although R is referred to as having a definite number of car-bon atoms, generally when alcohols are used to provide the alkyl group, a mixture of alcohols having various numbers of carbon atoms are used. These mixed alcohols, however, even when given as having a definite chain length actually average the values stated.

The primary and secondary alcohols can be used to provide the alkyl group in producing the alkyl polyoxyalkylene ether surfactants. Alkyl polyoxyalkylene ethers produced from the mixed primary alcohols having from 10 to 16 carbon atoms have been found to have especially good detergent properties. Alkyl polyoxyalkylene ethers produced from the secondary alcohols having a similar number of carbon atoms have also been found to demonstrate effective detergent properties but seem to be somewhat more heat sensitive than the foregoing ethers produced from the primary alcohols.

In most instances in producing the alkyl polyoxyalkylene ethers from about 3 to about 30 mols of alkylene oxide per mol of alcohol are used. It has been found that the alkyl polyoxyalkylene ethers of Formula A wherein m is relatively low such as below 5 are more heat sensi tive than those where m is a higher number such as 8 or larger, thus it is generally preferred to use from about 8 to about 20 mols of alkylene oxide per mol of alcohol when such a method is used to prepare the alkyl polyoxyalkylene ethers. The lower alkylene oxides such as ethylene oxide and propylene oxide are generally preferred with ethylene oxide being especially preferred. 11- lustrative of the alkyl polyoxyalkylene ethers which have been found to have suitable surface active properties produced by the condensation of an alcohol with an alkylene oxide include the product obtained from condensing 9 mols of ethylene oxide per mol of dodecyl alcohol; the condensation product of 8 mols of ethylene oxide per mol of tridecyl alcohol; the product obtained from condensing 10 mols of propylene oxide per mol of tetradecyl alcohol; and the condensation product of 12 mols of ethylene oxide per mol of 1,2-dodecanediol.

In most instances in practicing this invention, there will probably be employed other detergent additives such as the well-known phosphate builders sodium sulfate, silicates, optical brighteners, corrosion inhibitors, anti-redeposition agents, and the like to thereby form a detergent composition which would be subsequently heat dried. However, this invention is not so limited. The stabilization improvement of this invention is not dependent upon the presence or absence of other detergent additives.

The degree of sensitivity of the alkyl polyoxyalkylene ethers to oxygen and heat depends upon the degree of branching of the alkyl group with the sensitivity being decreased with an increase in branching. Although normally where an alkyl having a high degree of branching is used there will not normally be as great a need for use of the stabilizer compositions of this invention, some stabilizatron improvement can be achieved even with the highly branched, alkyl polyoxyalkylene ethers. By highly branched, it is meant that greater than about 15% of the carbons in the alkyl group are CH groups. Nuclear mag netic resonance analysis of the source of the alkyl group, such as the alcohols, can be used to determine the degree of branching. Furthermore, since the relatively straight chain material tends to be more biodegradable, it is preferred to produce the alkyl polyoxyalkylene ethers from compounds which will yield a relatively straight chain alkyl group. i

The compounds which have been found to provide stabilization to the alkyl polyoxyalkylene ethers are those selected from the group consisting of stabilizers represented by the following formulae.

H O l (CHa)a--C Formula 1 6-tert-butyl,3 1nethylphenol :)a (CHah? HO- (EH3 OH o113 3o H} CH o or-r3 H3O -CH3 l CH2 (CHQaC- C (CH3)3 OH Formula 2 1,3,5 trimethyl 2,4,6 tris(3,5 di-tert-butyl-4-hydroxybenzyl)benzene monophenolic compounds represented by the formula R Formula 3 wherein R is selected from the group consisting of CH OCH NH HNC(CH and CHgOH, n is an integer from 1 to 3; diphenolic compounds represented by the formulae Formula 4 Formula 5 wherein R is a bivalent radical selected from the group consisting of S and lower alkylidene; nitrogenous compounds represented by the formula HII\IR" Formula 7 wherein R and R" each are selected from branched chain alkyl radicals containing from about 3 to about 10 carbon atoms and phenyl; trimethylquinoline compounds represented by the formula Formula 8 wherein R is selected from the group consisting of alkoxy containing from about 2 to about 4 carbon atoms and alkyl containing from about 10 to about 14 carbon atoms and mixtures of the foregoing stabilizers.

Illustrative of useful monophenolic compounds represented by Formula 3 include 2,6-di-tert-butyL4-methyl phenol 2,6-di-tert-butyl-4-methoxy phenol 2,6-di-tert-butyl-4-amino phenol N-tert-butyl-2,6-di'tert-butyl-4-arnino phenol 4-hydroXymethyl-2,6-di-tert-butyl phenol 2-tert-butyl-4-methoxy phenol 3-tert-butyl-4-methoxy phenol 2-tert-butyl-4-methyl phenol 2,3,6-tri-tert-butyl-4-methoxy phenol Illustrative of the useful diphenolic compounds represented by Formulae 4, 5 and 6 include 4,4'-thio bis (3-rnethyl, 6 tert butyl phenol) 4,4'-methylene bis(3-methyl, 6-tert butyl phenol) 4,4-butylidene bis(3-methyl, 6-tert-buty1 phenol) 4,4'-ethylidene bis(3-methyl, 6-tert-butyl phenol) 4,4'-thio-bis(2-methyl-6-tert-butyl phenol) 4,4-methylene bis(2-methyl-6-tert-butyl phenol) 4,4-thio bis 2,6-di-tert-b utyl phenol) 4,4'-methylene bis (2,6-di-tert-butyl phenol) 4,4-butylidine bis(2,6-di-tert-butyl phenol) Illustrative of the useful nitrogenous compounds represented by Formula 7 include N,N' diphenyl-p-phenylenedia rnine N,N bis( l-ethyl-3-methyl pentyl)p-phenylenediamine N-isopropyl-N'-phenyl-p-phenylenediamine N,N'-bis( l-methyl'heptyl)p-phenylenediamine N,N-di-sec butyl-p-phenylenediamine N,N-di-isopropyl-p-phenylenediamine N,N'-di-tert-butyl-p-phenylenediamine Illustrative of the useful trimethylquinoline compound represented by Formula 8 include 6-ethoXy-1,2-dihydro-2,2,4-trimethylquinoline 6-dodecyl-1,2-dihydro-2,2,4-trimethylquinoline 6-tetradecyl l ,2-dihydro-2,2,4-trimethylquinoline 6-butoxy-1,2-dihydro-2,2,4-trimethylquinoline 6-decyl-1,2-dihydro-2,2,4-trimethylquinoline The choice of a particular stabilizer compound from the foregoing group of useful compounds will depend largely upon the drying temperatures used in drying the ether. In general, any temperature above about C. can be used to heat dry the alkyl polyoxyalkylene ether although in most instances temperatures above C. are used and more preferably temperatures from about C. to 220 C. in most spray drying operations. In some heat drying operation temperatures may be higher such as 250 C. or even 300 C. Although any of the foregoing classes of compounds give a discernible improvement in stability at relatively high drying temperatures such as C. or even higher such as 250 C. when incorporated into the alkyl polyoxyalkylene ethers in amounts of at least about 500 p.p.m., certain of the Of these compounds 6 ethoxy 1,2 dihydro 2,2,4 trimethylquinoline; N isopropyl,N-phenyl-p-phenylenediamine; N,N diphenyl p-phenylenediamine; 4,4"butylidene bis(6 tert-butyl-3-methylphenol); 1,3,5-trimethyl- 2,4,6-tris(3,5-tert-butyl-4-hydroxy benzoyl)benzene; 4,4- methylene bis(2,6-di-tertbutyl phenol); and 4,4-thiobis (6 tert-butyl-3-methylphenol) are preferred. At the lower temperatures that is from about 100 C. to about 170 C., all of the stabilizers of the Formulae 1-8 give an excellent improvement in heat sensitivity.

It is to be noted that although some of the compounds give a noticeable improvement in sensitivity, they can darken the alkyl polyoxyalkylene ethers due to the color of the heat stabilizer. In general, compounds which have a dark color and hence tend to darken the alkyl polyoxyalkylene ethers are those represented by Formulae 7 and 8. In some cases the degree of darkening may not be objectionable since small quantities are used. It is also possible to mask this darkening with the use of dyes in some applications. It is also to be noted that in some instances the color problem with some of the heat stabilizers can be minimized by operating within certain pH ranges.

It is, therefore, preferred when practicing this invention to use compounds represented by Formulae 2, 4, 5, and 6 so as to avoid color problems and to provide stabilization even at the higher drying temperatures. Of these, it is preferred. to use compounds represented by Formulae 2, 4, and 6.

Amounts as low as 500 ppm. can be used to achieve a discernible improvement in stabilization of the alkyl polyoxyalkylene ethers. However, it is generally preferred to employ the stabilizer in amounts greater than 1,000 ppm. based upon the weight of alkyl polyoxyalkylene ethers. It has generally been found that it is preferred to use from about 2,000 ppm. to about 5,000 ppm. of the stabilizer. Amounts greater than 5,000 ppm. for example 50,000 ppm, can be used but do not in most instances provide an amount of increased stabilization to warrant the higher level of usage.

The stabilizers of this invention can be added in any convenient manner to the alkyl polyoxyalkylene ethers. For example, when the foregoing surface active agents are used in a detergent formulation which are formulated in an aqueous slurry and subsequently dried, the stabilizer can be incorporated into the formulation at any convenient point prior to drying. It is only necessary that the heat stabilizers be present at the time the a kyl polyoxyalkylene ether is subjected to the temperatures heretofore given.

One method of employing this invention has been found to give'a particularly desired improvement in a spray drying operation. The alkyl polyoxyalkylene ethers were found to degrade in spray towers due to a tendency to cake upon the walls of the tower and thus be subjected to prolonged heating at relatively high temperatures. This problem was particularly acute when a concurrent flow spray drying tower was used. By employing the stabilizers of this invention a sufficient reduc* tion in the degradation of the alkyl polyoxyalkylene ethers is achieved to enable high quality material to be produced even after relatively long exposures to high temperatures.

Example 1 An alkyl polyoxyethylene ether composition is prepared by condensing ethylene oxide and a mixture of straight chain primary alcohol containing from 12 to 15 carbon atoms and having an average chain length of 13. About 7 to moles of ethylene oxide are used per mole of the mixed alcohols calculated on the basis that all of the alcohols contained 13 carbon atoms so that the surface active agent can be represented by the following formula:

TABLE I.EFFECT OF STABILIZERS Stabilizer Weight Loss,

Percent None N,N' bis(l-ethyl-3 methylpentyl)-p-phenylenediamine.

6 ethoxy-1,2-dihydr0 2,2,4 trimethylquinoline...

N-isopropyl N -phenyl-p-phenylenedlamine 4,4 butylidene (titert-butyl-B-methyl phenol) N,N-diphenyl-p-phenylenediamine, 25% (i-dodecyl 1,2-dihydro-2,2,4trlmethylquinoline. N-butyl-p-aminophenol N,N-di-see butyl-p-phenylene diamine. 4-hydroxymethyl-2,6di-tert-bntyl phenol 4,4-methylene bis(2,6-di-tert-butylphenol) 4,4-methylene bis(2,6-di-tert-butyl-4 hydroxy be izyl) benzene. N,N-dipheny1-p-phenylenediamine Gdodecyl-LZ-dihydro 2,2,4 trimethyl quincine 4,4-thiobis (6 tert-butyl-3-rnethylphenol) N ,N-diisopropyl-p-phenylenediamine 2,6-di-tert butyl-4-methylphenol It is evident from the results of the foregoing tests that the degradation of the alkyl polyoxyethylene ethers is elfectively reduced by the practice of this invention. It is to be noted that Samples 5, 9, 14 and 16 are clear before and after heating. Some color change occurs in the other samples upon incorporating the stabilizer before heating. Similar reductions in degradation occur when similar amounts of the foregoing degradation inhibitors are incorporated into other alkyl polyoxyalkylene ethers.

Example 2 The procedure used in Example 1 is followed except that the alkyl polyoxyalkylene ethers are heated at C. for 2 hours. The following table gives the results of the tests.

TABLE II Weight Loss, Percent Sample Stabilizer 1,000 2,000 p.p.m. p.p.m.

1 None 4. 0 2 N,N his (l ethyl-il-rnethylpentyl) 2. 3 .0

-phenylenediamine. 3 75%, N,N diphenyl-p-phenylenedi- 1.1 1. 1

' amine, 25% 6-dodecyl 1,2-dihydro- 2,2,4-trimethylquinoline. 4 4,4-thiobis(G-tert-butyl-B-methyl 1. 4 1. 2

phenol). 5... 4,4 butylidene(fi tert-butyl-li-methyl 1. 5 0. 9

phenol 6 1,2 dihydro-2,2,4-trimethylquino- 1. 3 1. 2

me. 7 Mixture of 2-tert butyl4-methoxy 1.0 1.1

pgeuol and 3-tertbutyl'4-methoxy p en 8 2-tert-butyl-4-methylphen0l 2. 8 1. 4 9 2,6-di-tert butyl-4methylphenol. 2. 6 1. 8

All samples which have the stabilizers have significantly less weight loss than the sample without the stabilizer. Samples 1, 4, 5, 6, 7, 8 and 9 are clear before and after heating while Sample 2 is pink and Sample 3 is grey.

7 Example 3 Into a detergent crutcher are charged the ingredients:

following product of ethylene oxide per mole of dodecyl alcohol) 150 The foregoing material is mixed thoroughly in the de tergent crutcher and pumped to a conventional spray tower and dried with heated air at about 180 C. and is dried to form a solid detergent product containing about by weight of Water. The foregoing material tends to cake on the walls of a spray tower and when removed after about 24 hours continuous operation, analyses of the material indicates about 50% by Weight of the alkylene ether has been degraded.

When the detergent formulation given above is stabilized with about 3,000 p.p.m. of 4,4-methylene-bis-2,6- (di-tert-butyl phenol) based on the weight alkyl polyoxyethylene ether by incorporating the stabilizer into the detergent crutcher prior to spray drying the alkyl polyoxyethylene ether content of the material that is caked on the walls shows less than about 10% reduction in active content after exposure of 24 hours. Substantially similar results are achieved when the stabilizers employed in samples 4, 5, 6, 7, 8 and 9 of Example 2 are used in similar weight amounts. It is to be noted that even when the detergent additives are present the stabilizer eifectively reduces the amount of oxidation of the alkyl polyoxyethylene ethers.

What is claimed is:

1. In the process for heat drying an alkyl polyoxyalkylene ether surfactant in the presence of air at temperatures above about 100 C. the improvement comprising incorporating into said alkyl polyoxyalkylene ether prior to said heat drying at least about 500 parts per million by weight, 'based upon said surfactant, a stabilizer compound selected from the group consisting of those represented by the following formulae wherein R is selected from the group consisting of CH OCH HNC(CH and CH OH, and n is an integer from 1 to 3;;

wherein R is a bivalent radical selected from the group consisting of S and lower alkylidene;

HIV-R wherein R' and R" are each selected from branched chain alkyl radicals containing from about 3 to about 10 carbon atoms and phenyl; and

wherein R is selected from the group consisting of alkoxy containing from about 2 to about 4 carbon atoms and alkyl containing from about 10 to about 14 carbon atoms and mixtures of the foregoing stabilizers.

2. A process according to claim 1 wherein said surfactant is represented by the formula wherein R is an alkyl radical containing from about 6 to about 24 carbon atoms, Z is selected from H, 80.; and P0 n is an integer from 2 to 4, x is an integer from 1 to 2, m is an integer from 1 to 29 when x is 1, and m. is an integer from 1 to 14 when x is 2, and the amount of heat stabilizer is at least about 2,000 p.p.m.

3. A process according to claim 2 wherein said sur- 0 factant n is from 2 to 3 and Z is OH.

4. A process according to claim 3 wherein said stabilizer is a trimethylquinoline compound represented by the formula and alkyl containing from about 10 to about 14 carbon atoms and mixtures of the foregoing stabilizers.

5. A process according to claim 3 wherein said stabilizer is a monophenolic compound represented by the formula wherein R is selected from the group consisting of' wherein R and R" each are selected from branched chain alkyl radicals containing from about 3 to about carbon atoms and phenyl.

9. A process according to claim 8 wherein R and R" are each phenyl.

10. A process according to claim 3 wherein said stabilizer is a diphenolic compound represented by the formula wherein R is a bivalent radical selected from the group consisting of S and lower alkylidene.

11. A process according to claim 10 wherein R in said stabilizer is S.

12. A process according to claim 10 wherein R in said stabilizer is butylidene.

13. A process according to claim 3 wherein said stabilizer is 4,4-methy1enebis-2,6-(di-tert-butylphenol).

14. A process according to claim 3 wherein said stabilizer is 1,3,5-(trimethyl-2,4,6-tris,3,5, di-tert-butyl-4-hydroxybenzene) 15. A process according to claim 3 wherein said stabilizer is 4-hydroxymethyl, 2,6-ditert-butylphenol.

References Cited UNITED STATES PATENTS 2,692,877 10/1954 Gray et al. 34,-9 X 2,917,833 12/1959 Kremen et al. 34-9 FREDERICK L. MATTESON, 111., Primary Examiner.

JOHN J. CAMBY, Examiner. 

1. IN THE PROCESS FOR HEAT DRYING AND ALKYL POLYOXYALKYLENE ETHER SURFACTANT IN THE PRESENCE OF AIR AT TEMPERATURES ABOVE ABOUT 100*C. THE IMPROVEMENT COMPRISING INCORPORATING INTO SAID ALKYL POLYOXYALKYLENE ETHER PRIOR TO SAID HEAT DRYING AT LEAST ABOUT 500 PARTS PER MILLION BY WEIGHT, BASED UPON SAID SURFACTANT, A STABILIZER COMPOUND SELECTED FROM THE GROUP CONSISTING OF THOSE REPRESENTED BY THE FOLLOWING FORMULAE 